1. Field of the Invention
The present invention relates to an inner cutter for a rotary shaver and to a rotary shaver that uses the same and more particularly to an inner cutter for a rotary shaver in which the material thereof can be made thin and which exhibits outstanding anti-wear properties and to a rotary shaver using such an inner cutter.
2. Description of the Related Art
In electric shavers, such as rotary shavers, the relationship between the anti-wear properties (feel of the shave) and the designing of the material to be thin is generally a relationship of a trade-off to take only one of the two. In other words, when priority is given to anti-wear properties, it becomes very difficult to make the material thinner and inner cutter manufacturing costs go up, whereas, when designing the material thinner is given priority, then it becomes difficult to realize anti-wear properties and product value declines. Accordingly, in general, for inner cutters and rotary shavers placed on the market, a balance is maintained between anti-wear properties and designing of the material to be thinner in inner cutters.
In order to effect good shaves with an inner cutter for a rotary shaver in which such a balance is taken between anti-wear properties and designing of the material to be thinner, cutter blades of inner cutter are usually inclined in the direction in which the inner cutter rotates as shown in, for instance, FIG. 6 of Japanese Patent Application Laid-Open (Kokai) No. 2005-185827. The reason for the inclined cutter blades is that, by taking the shape like that of FIG. 6 in Japanese Patent Application Laid-Open (Kokai) No. 2005-185827, it becomes possible to effect good shaves even with a thin-material structure.
Here, the structure in which the cutter blades of the inner cutter in a rotary shaver are inclined in the direction of rotation of the inner cutter means that the position of the leading tip end portions (or leading edge portions) of the cutter blades of the inner cutter are located forward, relative to the base portions thereof, in the direction of rotation of the inner cutter.
When the inner cutter for a rotary shaver is thin, such a measure is sometimes implemented that an inner cutter guide vibration-preventing member which is for supporting the lower surface of the inner cutter main body is provided in an inner cutter guide that connects the inner cutter to the output shaft of a drive means provided in the rotary shaver, so that, the lower surface of the inner cutter main body is supported thereby, and thus preventing vibration when the inner cutter is rotated.
However, when the inner cutter for a rotary shaver such as that shown in Japanese Patent Application Laid-Open (Kokai) No. 2005-185827 is rotated, minute vibrations tend to occur in the cutter blade supports (the elements 118 in Japanese Patent Application Laid-Open (Kokai) No. 2005-185827) of the inner cutter due both to friction caused by the blade surface sliding resistance between the outer cutter and the inner cutter and to shaving resistance. As a consequence, there are such problems that abnormal wear occurs in the portions of the blade surfaces of the outer cutter and inner cutter that slide against each other and that the feel of the shave deteriorates. In some cases, moreover, the rotary shaver is damaged and not usable any longer.
In the following, minute vibrations that would occur in the inner cutter (or inside the cutter blades of inner cutter) will be described. FIG. 15 shows illustrations that represent a blackboard and a piece of chalk when a line is being drawn on the blackboard with the chalk.
As shown in Illustration A of FIG. 15, when the chalk is slanted toward the blackboard, and the chalk is moved in the direction of the arrow while lightly pressing the chalk against the blackboard (advancing in a direction from the end of the chalk being held by hand toward the end of the chalk that is in contact with the blackboard), stuttering occurs due to the relationship between the force of friction, which is between the blackboard and the chalk, and the force with which the chalk is being pressed. As a result, an intermittent movement phenomenon would occur so that the chalk skips over the blackboard (such phenomenon will be called “chalk phenomenon”) as shown in Illustration B of FIG. 15.
When the force that the chalk is pressed against the blackboard and the speed of movement of the chalk is held constant, then the way the chalk phenomenon occurs will be different depending on the angle of inclination α of the chalk to the blackboard. In other words, when the angle of inclination α of the chalk relative to the blackboard is small as shown in Illustration C of FIG. 15, the chalk phenomenon will not readily occur. When, on the other hand, the angle of inclination α of the chalk relative to the blackboard is great as shown in Illustrations D and E of FIG. 15, the chalk phenomenon will readily occur. When, however, as shown in Illustration F of FIG. 15, the chalk being pressed against the blackboard is moved in a direction opposite the direction of chalk movement as shown in Illustration F of FIG. 15, even when the angle of inclination of the chalk relative to the blackboard is about the same as this angle of inclination in Illustration F of FIG. 15, the chalk phenomenon will not occur.
This so-called “chalk phenomenon” described above is not a phenomenon that occurs only between a blackboard and a piece of chalk, but it would occur similarly in metals, plastics, and wood materials and the like. Furthermore, as shown in Illustration G of FIG. 15, the greater the length of the moving body, and the greater ease wherewith deflection occurs in the moving body, the greater the tendency would be for the chalk phenomenon to occur in a pronounced way.
Also, in electric shavers, because such measures as attaching inner cutter guide vibration-preventing members as described earlier, or designing the inner cutter sheet thickness thicker are implemented as general techniques for extending the useful life of inner cutters, there is a problem of soaring inner cutter manufacturing costs.
Furthermore, in response to the demand for cleanliness, most electric shavers, including rotary shavers, in recent years, are products that can be washed in water. In almost all of these electric shavers that can be washed in water, the cutters are moved (rotated, or reciprocated in reciprocating shavers) in an unoiled condition after washing. When the cutters are, for instance, rotated in such an unoiled condition, additional loads are placed on the inner cutter and outer cutter, causing a problem that wear between the inner cutter and outer cutter is accelerated. Because inner cutters and outer cutters are used in such severe conditions, it may now be said that hair cutting sharpness deteriorates in a shorter time than with conventional rotary shavers.